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Department of Psychology, Simon Fraser University, Burnaby British Columbia, Canada V5A 1S6
Induced and spontaneous wheel
running can alter the phase and period (
) of circadian rhythms in
rodents. The relationship between spontaneous running and the phase
angle (
) of entrainment to 24-h light-dark (LD) cycles was evaluated
in C57BL/6j mice. With a wheel freely available,
was significantly
correlated with the absolute (r = 0.32) and relative
(r = 0.44) amount of activity during the first 2 h of
the activity period. When wheels were locked during the first half of
the night in LD and then unlocked in constant dark (DD), mice exhibited
a delayed
and lengthened
compared with mice that had wheels
locked during the second half of the night. In DD,
correlated
negatively with total daily activity. To evaluate if wheel running
modulates the phase-resetting actions of LD, phase shifts to light
pulses were measured at two time points in DD, when daily activity
levels differed by 40%. Phase delays to light were 56% greater when
activity levels were lower. However, in a counterbalanced follow-up
experiment, phase advances and delays to light pulses were not affected
by the availability of wheels, although an effect of time in DD was replicated. Spontaneous activity can regulate
and
without altering the response of the pacemaker to light.
wheel running; entrainment; nonphotic zeitgeber; phase shifts; light pulses
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